This study aims to evaluate the effect of countdown installation on traffic flow parameters. The case study is related to four intersections with countdown timers and four intersections without countdown timers in Isfahan city. In this survey, traffic flow parameters such as start-up lost time, saturation flow rate and saturation headway and also the drivers perception-reaction time with and without countdown timers were analyzed by using statics related to intersections. In analyzing headways, the mean of headway on the first vehicle of lanes and different intersections are reduced with using countdown timer in peak hours. While that headway on the first vehicle in off peak hour is larger than headway on the first vehicle in peak hours. The countdown timers do not have much impact on the first vehicle of headway in off peak hours. The result of standard statistical t-test show that saturation headway and saturation flow rate are not statically different at the 95% confidence interval for both the with timer and without timer conditions. It was found that the countdown timers reduced the start-up lost time in different intersections and also the lost time in Hasht behesht-Bozorgmehr and Hasht behesht-Hamzeh is other intersections. It is found that the time of field survey was done in peak hours of work and education, so the lost time has reduced. Also the impact of countdown timer on reducing lost time in Abshar and Freiburg intersections was remarkable in outing peak hours. In general, countdown timers reduce mean of PRT drivers 0/3 second. Also at various intesections, scattering data at the intersection with display was less than the intersection without display. The results indicated that Weibull distribution appeared to best fit the PRT with no timer and Gamma distribution appeared to best fit the PRT with timer. Distribution difference of PRT of drivers in different conditions shows that drivers behaviors are different in two situations. The fuzzy c-means clustering has been utilized for PRT justify; MARGIN: 0in 0in 0pt; unicode-bidi: embed; DIRECTION: ltr" dir=ltr Key words: Countdown, Perception–reaction time, Distribution fitting, Headway, clustering, Lost time
